Last night, I was humming in the shower of my cheap motel in Monterey. As I hit a low note in my little ditty, the volume of my song jumped substantially. I was a bit surprised, but thankfully I understood why this occurred. I had unintentionally found the fundamental mode's frequency for this shower.
I should explain that the geometry of this shower is unconventional. The showers in this cheap motel are 6'6" tall, 3' wide, 4'6" long tiled rectangular prisms with a thin glass door on hinges. It's a dark, claustrophobic shower cavity and a decent approximation of a Helmholtz resonator.
The fundamental mode of a rectangular cavity depends on the two larger dimensions and if you know the speed of sound in the box, you can calculate that frequency. I found it to be about 178 Hz. I was humming the song shown below and the low note that caused the resonation was E on the 2nd standard octave. This is about 82.4 Hz. 82.4 times 2 is pretty close to 178 Hz, so I reckon my estimates on the dimensions of the shower chamber are off.
Anyways, it's interesting to think about how air carries sound and how one might manipulate that fact to change the volume.
Photos from the aquarium: https://photos.app.goo.gl/ikHixXCPF6CJDUzy9
The acoustic frequencies of importance
Some notes on resonant frequencies